The robber apparently went down into the subway with his loot after fleeing the bank, but a security dye pack exploded, prompting the Fire Department to call a hazardous materials response, the FBI said.

Following the dye pack explosion, Red Line trains were rerouted to the Brown-Purple Line ‘L’ tracks between the Fullerton Avenue and Cermak-Chinatown stations.

The FBI had a suspect in custody as of 12:15 p.m.

WBBM Newsradio’s Bart Shore said trains were returning to the subway as of 11:49 a.m.

Police activity was also reported at the Chicago-Franklin CTA Brown Line stop. It was not clear if this was connected to the same incident.